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Blowing up coils

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I keep blowing coils on my 82 Brat, I did a search and have conversed with Bill and a few others but still I can get it to run for more than 17 mins before it pops another coil. I have replaced the dist, the alt. the coil(s) and even made sure there was a red fusable link in the right area..........

 

I'm almost at a loss here, I tried 3 different distys but I have no Idea, everthing reads right on the voltage and everthing. I just dont know........

 

any help would be good

 

Jeff

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Unless they are just bad coils(same brand?)(incorrect ballast resistor type?) or the mounting subjects them to unusual heat or vibration,the problem is probably excessive resistance in the ignition secondary circuit.This will make the coil produce higher than normal voltage,

 

Check plug gaps,plug/coil wire resistance,disty rotor cap clearance etc.

You may want to try a different capacitor too.

 

Conversly,if your ignition system has the external type ignition module,a ballast resistor is required.A missing one would blow coils.

Are they hot after they blow?

 

Even a lean mixture will make the voltage higher than normal.

 

Good luck.

Edited by naru

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They are not hot at all, just dont make spark anymore, as for the resistor, Its not set up,I have it set up the exact same as my other 82 Brat, yet this one dont work too well...........

 

Jeff

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Check yer grounds?

 

I second that, somethings grounding out somewhere.

 

Interesting, I wanna know the answer.

Good luck Jeff.

 

-Tom

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I suspect that a ballast resistor is missing so the current is too high to the primary side of the coil and burning it up. I think the voltage to the coil should be less than 10 volts when in the RUN mode. The original coil may have a internal resistor possibly. I don't know for sure.

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I got a stock pile of coils yesterday, so Tomorrow I am going to dive in head first and fugure this out...................... I will post up what I find.....

 

Jeff

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Subaru's do not use ballast resistors. They are designed to work at full VR output and still fire well enough to start the engine on battery voltage.

 

GD

 

Another typicaly oversweeping incorrect assertion.

 

Some at least,do indeed have ballast resistors.

Not sure about 82s but he says he has one and Chiltons shows one.

Some slightly older models definetly have one.

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Doesn't Vr = Voltage Regulator? Whether you have a internal or external voltage regulator it's tied to the alternator and battery.

 

That being said .... To start a car when the engine is cold most cars need more voltage at the coil than when a car is already running. Many cars 1950's and older used 6 volt starting systems and generators not alternators. Compression was low like 6 to 1 or less and the number of cylinders was 4 or 6. Even gasoline was crappy back then having real low octane ratings. These cars could be very hard to start on cold mornings if your battery wasn't in real good shape. This is why ether was used to start cars.

 

It was then realized if they went to 12 volt batteries the engines turned over faster and more voltage was available for the ignition system. Hence the car started real quick every time. Problem was the points were burning up. So auto engineers used a ballast resistor to limit/reduce the voltage to the points and coil to 6 volts. There was an additional wire directly from the ignition switch that allowed 12 volts just for starting not running. This allowed the coil to run cooler and points to not burn up so fast. Some ballast resistors limited voltage to 8 volts and some to 6 volts. That was the purpose for a ballast resistor. Most cars now days used a resistor wire with a bypass wire for starting only. I hope this helps with understanding old systems a bit.

Edited by Delta Brat
Added Statement of compression

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That post was only an overview of sorts. There are many ignition systems and starting systems out there and by no means did I cover hardly any of them.

 

Keep in mind the free things are always a good place to start. Clean your cables and connections. Then check for voltages at the coil. If you have 12 volts at the coil then I would look at how much is it supposed to have? Is your ignition switch still supplying 12 volts and causing the coil to burn up?

 

Thats where I would start.

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If the design of the ignition system didn't include a ballast resistor then we have to figure out what else is causing the trouble. The only thing I can think of is the charging system my be inducing some excessive AC ripple due to bad diodes in the alternator. To see if that is the case check the voltage across the battery while the engine is running using a digital meter set to AC volts and see if there is more than .1 volt AC present.

 

Edit:

Another thought about what may be happening here is something besides the disty is tied to the minus side of the coil and drawing excessive current through the coil. Like the tach circuit possibly.

Edited by Cougar

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So I, with a quite a bit of help, Figured it out. The fuse for the Ign-Coil is supposed to be a 15amper and someone had a 20amp fuse in its place. With that being said, I hooked the radiator fan up to a harness with power so it would run full time, that harness ran off the same fuse as the coil and ign. after the Brat would run for close to 20 mins with the fan and motor running the Coil would crap out, Once We plugged the fan in and had the smaller 15 amp fuse in it would blow the fuse, So I figure that the coil was not getting the correct voltage while running and over working the coil to make spark......................

 

Jeff

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I have to question your explanation on this. Fuses do not control voltage, they limit current to a safe level to protect the wiring and devices they supply current to. There is still 12 volts getting to the devices with either size fuse. The current load on the fuse will determine if it will blow or not, not the voltage. If the fans were connected to power through the coil then they would not have full voltage getting to them because of the series voltage drop through the coil. This would slow the fan speed down and cause much more current draw through the coil than it should have.

 

If the fans were connecting up to power through the coil I then could understand what is happening because of the extra current draw the fans would have made through the coil. This is the kind of thing I was refering to in my last post on this issue. Something appears to be drawing extra current through the coil. I would be checking all connections to the negative side of the coil for the trouble.

Edited by Cougar

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Low voltage wouldn`t blow coils either.

 

Spiky back emf from a worn high current motor on the same circuit would be problematic though.

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Well there is an update.....................

It stopped working again.............................................

 

And I'm again back to square one.........

 

Jeff

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Did you check out the leads that are connected to the minus side of the coil? If there is anyother lead tied to that point except the lead to the disty then disconnect it. Another thing you should test is the resistance to ground on any the leads tied to the minus side of the coil. Check the resistance of each while they are disconnected from the coil. A low resistance to ground will cause this kind of trouble.

 

To be sure, I assume you are connecting the wiring coming from the ignition power to the PLUS side of the coil and the MINUS side to the disty.

Edited by Cougar

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Some time back I wired my fan to the terminal on the coil for positive battery (while I was rewireing a system) and when the fan would start the engine would die. It didn't ruin the coil, but would kill the engine. My idea was that the fan motor was pulling too much current and would not leave enough for the engine to run on. I changed the position of the fan wire and it worked just fine.

Is your coil blowing up like KERPOWWW or just getting hot and not working??? I don't remember how to hook up the Subaru dist to the coil, but on a VW the points or dist hooks to the Negitive terminal.

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Accessories like the fans should never be tied to the ignition circuit. I suspect the problem you had could be due to a weak voltage getting to the coil. Especially if there was a ballast resistor in the circuit. The motor current from the fan would cause most of the voltage to drop across the resistor and leave very little for the coil.

 

Subarus use the minus side of the coil also to run the ignition pulses.

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